The present invention relates to a new disk drive, and particularly to a disk drive in which a self-aligning mechanism for canceling an unbalance of a recording medium disk is provided in a rotation drive portion for rotating the recording medium disk, wherein the self-aligning mechanism is improved to certainly achieve the function thereof.
The schematic configuration of one example of a related art disk drive is shown in FIGS. 1 and 2.
A disk drive "a" includes a mechanical chassis "b" on which necessary members and parts are mounted.
A spindle motor "d" for rotating a turn table "c" is disposed on one end portion of the mechanical chassis "b". An optical disk "e" is supported on the turn table "c" and is rotated by the spindle motor "d" together with the turn table "c". An optical pickup llgll is disposed on the mechanical chassis "b", which pickup is moved by a thread motor "f" in the radial direction of the optical disk "e" supported on the turn table "c". A drive unit "h" is configured by the mechanical chassis "b" on which necessary members and parts are disposed as described above. The drive unit "h" is mounted on a base chassis "j" via elastic bodies "i". The optical disk "e" is disposed in an unbalance state, that is, in a state in which the center of gravity is not positioned at the center of the mechanical chassis "b", and accordingly, when the optical disk "e" is rotated at a high speed, there occurs vibration. The reason why the elastic bodies "i" are interposed between the drive unit "h" and the base chassis "j" is to prevent such vibration caused by high speed rotation of the optical disk "e" from being transmitted to the outside of the disk drive "a".
A counter weight "k" is mounted on the mechanical chassis "b" on the side, on which the optical pickup "g" and thread motor "f" are disposed, with respect to a horizontal line H--H passing through the rotational center of the optical disk "e", that is, the rotational center "O" of the spindle motor "d".
The spindle motor "d" has a self-aligning mechanism.
The self-aligning mechanism of the spindle motor "d" functions on the basis of the following principle:
FIG. 3 shows a self-balancing device I as one example of the automatic self-aligning mechanism. The self-balancing device "I" includes a holder "m" having an annular race portion, and a plurality of balls "n" freely movable on the holder "m".
In the case where the optical disk "e" supported on the turn table "c" in the unbalanced state is rotated at a frequency higher than a resonance frequency of a vibration system composed of the drive unit "h" and the elastic bodies "i", the drive unit "h" is vibrated with its phase delayed approximately 180.degree. from the phase of the unbalance of the optical disk "e". Since the balls "n" are automatically moved in the direction in which the drive unit "h" is vibrated, that is, moved on the reversed phase side to the unbalance of the optical disk "e", the balance of the drive unit "h" is automatically kept by the movement of the balls "n".
If the drive unit "h" is vibrated by rotation of the optical disk "e" disposed in the unbalanced state, not only readout or writing of signals in or from the optical disk "e" may be not sufficiently performed but also the vibration, if it is transmitted to the outside of the disk drive "a", may exert adverse effect on the peripheral environment, for example, may induce vibration of peripheral equipment such as a hard disk drive, leading to malfunction thereof. However, the self-aligning mechanism provided on the spindle motor "d" makes it possible to prevent the above-described adverse effect.
Incidentally, in the related art disk drive "a", the counter weight "k" is mounted on the mechanical chassis "b" on the side, on which the optical pickup "g" and thread motor "f" are disposed, with respect to the horizontal line H--H passing through the rotational center of the optical disk "e", that is, the rotational center "O" of the spindle motor "d". The reason for this is as follows:
The position of the center of gravity G of the entire drive unit "h" is determined depending on the arrangement of the optical pickup "g", thread motor "f" and the like mounted thereon and the shape of the mechanical chassis "b" itself.
In the case where the center of gravity G is not positioned at the center of the drive unit "h", there occurs an inconvenience that if the mechanical chassis "b" is made from a resin material having a poor rigidity, the mechanical chassis "b" is largely distorted by vibration caused by high speed rotation of the optical disk "ee"disposed in the unbalanced state, with a result that the optical pickup "g" cannot correctly read information stored in the optical disk "e". This is due to the fact that there occurs a difference in vibration amplitude and vibration phase between the right and left sides of the mechanical chassis "b" resulting from the shifting of the center of gravity G from the center of the mechanical chassis "b", so that the mechanical chassis "b" is twisted. Accordingly, in order to shift the center of gravity G of the drive unit "h" to the center of the drive unit "h" itself, the counter weight "k" is disposed at the above-described position.
However, when the center of gravity G of the drive unit "h" is largely shifted from the rotational center "O" of the optical disk "e" as in the related art disk drive "a", vibration resulting from unbalance of the optical disk "e", that is, the orbit of vibration of the axis resulting therefrom becomes an elliptical orbit designated by symbol "o" in FIG. 2. The reason for this is that since the vibrational input is offset from the center of gravity, there occurs vibration of 2 degrees of freedom, because the system has both parallel vibration and rotational vibration.
If the orbit of vibration of the axis becomes an elliptical orbit, the operation of the self-aligning mechanism becomes unstable, failing to sufficiently achieve the performance thereof.
Further, as in the disk drive "a", even if the counter weight "k" is not provided, the center of gravity of the drive unit "h" is shifted from the rotational center of the spindle motor "d" to the side on which the optical pickup "g", thread motor "f" and the like are disposed, with a result that the orbit of vibration caused by high speed rotation of the optical disk "e" disposed in the unbalanced state becomes an elliptical orbit and thereby the self-aligning mechanism also fails to sufficiently achieve the performance thereof.
Accordingly, in the conventional disk drive, the self-alignment mechanism fails to sufficiently achieve the performance thereof irrespective of provision of the counter weight "k". This obstructs the rotational speed of a recording medium disk from being increased for making fast the transfer speed of data.